Reduce the number of used unstable features of x86_64 crate (#155)

* Reduce the number of used unstable features of x86_64 crate

To reduce nightly breakage.

* Update changelog

* Update tests/test_kernels/default_settings/Cargo.toml

Co-authored-by: bjorn3 <bjorn3@users.noreply.github.com>

* Fix dependency

* Run cargo update

Co-authored-by: bjorn3 <bjorn3@users.noreply.github.com>

Author: phil-opp